Bruno670,
When I was breaking in my '06 YZ125 that I ride in the tight woods, exclusively, I was very careful to make only one change at a time, (and still am!) I had backed my suspension clickers to near full soft, across the board, until things softened up a bit.
I had ridden on the stock tires several times, but now it was time to remove the factory rim protectors and replace them with something better. I decided to try some Michelins, and since I was attempting to do everything 'right' on this bike, I made sure to install "heavy duty" tubes, as well (*see note below.)
I rode the bike the same day, at the same trails that I had ridden my last ride. Of course I was focusing on the tires traction characteristics as I started out my ride, trying to compare. It seemed that the tires were working a bit better than my stockers, but not by as much of a margin as I had hoped.
Oh well, let's focus on my riding now; time to pick up the pace; lets ride!
I think is was on our 2nd loop, that I started noticing that on the higher speed bumps, the back end was 'kicking' up considerably. I was getting the the same sensation that my 1981 YZ250 used to exhibit, that the magazines at the time referred to as "Yama-kick"
It took me a while to realize that it was the extra weight (? 1-2 lbs.?) of the 'heavy' tubes I had installed.
I suppose that the heavier the bike one rides, the less noticeable this might be. I also noticed and understand that the Michelin tires seemed to have a stiffer sidewall (less flex, or give.) I also suspect that the heavy duty tubes increase the tire 'stiffness,' or lack of flex.
Bottom line, I figured out for myself, that tires and innertubes, can & do affect the way a bike rides, or "handles."
From my roadracing experience, I would bet that a back to back comparison of light & heavy tubes, at high speeds, would reveal a heavier steering feel, or resistance to turning, not to mention the need for different suspension settings.
The gyroscopic effect (precession?) is a quite noticable affect on a bike, but what I have been talking about is also discussed as comparing 'sprung weight' to 'unsprung weight."
*note: I learned this year that there are actually 3 grades of innertubes; regular (standard,) 'heavy duty,' and 'extra heavy duty.'
Good luck; experiment, & report back please!
Regards, Ken W.